This invention relates to the art of blow molding articles of organic plastic material from a parison and has for its principal object a method for obtaining improved, oriented hollow articles.
The art teaches various methods and apparatus for obtaining blow molded articles of organic plastic material from a parison, such as in U.S. Pat. No. 3,349,155 and Re. 27,104. Generally, these methods are characterized by forming a parison in a parison mold on a blow core, placing said formed parison and blow core into a blow mold and expanding said parison in the blow mold by means of fluid pressure.
Naturally, the blowing procedure inherently produces orientation in the plastic due to expansion in a radial direction; however, it is highly desirable to produce orientation in the axial direction as well. Heretofore, this has been done by re-heating the parison and, before blowing, axially orienting the parison, such as by stretching.
Such known methods are subject to disadvantages, such as the difficulty of maintaining uniform wall thickness. Obviously, control of wall thickness is quite important. Other difficulties include insufficient control of the parison dimensions and degree of orientation and time consuming and inconvenient operations.
This invention particularly relates to lined hollow articles formed from composite parisons having a preformed inner sleeve or lining, such as described in my prior U.S. Pat. Nos. 3,719,735 and 3,717,544. According to said patents, a previously formed, sleeve-like liner is applied to a blow core of an injection blow molding apparatus, plastic is injected around said liner while upon the core and the resultant composite parison, consisting of the liner and the injected plastic is expanded together into conformity with a blow mold.
It is highly desirable to obtain a lined article as aforesaid, wherein both layers of the article have orientation in the axial as well as radial direction. It is also desirable to produce such an oriented, lined hollow article simply and conveniently, without the disadvantages known heretofore.
Accordingly, it is a principal object of the present invention to provide a method for obtaining a lined hollow, plastic article having orientation in the axial, radial and tangential directions.
It is a further object of the present invention to provide a method as aforesaid which is simple and convenient to utilize, readily adapted to commercial operation and results in an improved, oriented hollow plastic article.
Further objects and advantages of the present invention will appear from the ensuing specification.